Gen Sazaki

Effects of a magnetic field on the nucleation and growth of protein crystals

Crystallization of hen egg-white lysozyme and horse-spleen ferritin was carried out under a steady and uniform magnetic field of 10 T and compared with the crystals grown under 0 T. It is clearly demonstrated that a magnetic field reduced the number of nuclei and not only oriented the crystals but also modified the habit of protein crystals. The present experimental result indicates that application of a magnetic field is an efficient method for growing a small number of large crystals.

Crystal Structures of the Reaction Intermediate and its Homologue of an Extradiol-cleaving Catecholic Dioxygenase

BphC derived from Pseudomonas sp. strain KKS102 is an extradiol-cleaving catecholic dioxygenase. This enzyme contains a non-heme iron atom and plays an important role in degrading biphenyl/polychlorinated biphenyls (PCBs) in the microbe. To elucidate detailed structures of BphC reaction intermediates, crystal structures of the substrate-free form, the BphC-substrate complex, and the BphC-substrate-NO (nitric oxide) complex were determined. These crystal structures revealed (1) the binding site of the O(2) molecule in the coordination sphere and (2) conformational changes of His194 during the catalytic reaction. On the basis of these findings, we propose a catalytic mechanism for the extradiol-cleaving catecholic dioxygenase in which His194 seems to play three distinct roles. At the early stage of the catalytic reaction, His194 appears to act as a catalytic base, which likely deprotonates the hydroxyl group of the substrate. At the next stage, the protonated His194 seems to stabilize a negative charge on the O2 molecule located in the hydrophobic O2-binding cavity. Finally, protonated His194 seems to function as a proton donor, whose existence has been proposed.

Enhanced quantum efficiency of solar cells with self-assembled Ge dots stacked in multilayer structure

We report on the performance of solar cells with stacked self-assembled Ge dots in the intrinsic region of Si-based p-i-n diode. These dots were epitaxially grown on p-type Si(100) substrate via the Stranski–Krastanov growth mode by gas-source molecular beam epitaxy. Enhanced external quantum efficiency (EQE) in the infrared region up to 1.45 μm was observed for the solar cells with stacked self-assembled Ge dots compared with that without Ge dots. Furthermore, the EQE was found to increase with increasing number of stacking. These results show that electron-hole pairs generated in Ge dots can be efficiently separated by the internal electric field, and can contribute to the photocurrent without considerable recombination in Ge dots or at Ge/Si interfaces.

Elementary steps at the surface of ice crystals visualized by advanced optical microscopy

Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.

A novel approach to the solubility measurement of protein crystals by two-beam interferometry

Abstract A novel technique was developed for the rapid solubility measurement of protein crystals (lysozyme) by two-beam interferometry. The merits of this technique are: (1) time saving (less than 2 h to obtain one experimental point), (2) the small amount of the sample (∼66 μl), (3) high accuracy, (4) applicable to the solubility measurement of a metastable phase and (5) insensitive to impurities. The limitations of the present technique are also discussed.

Effects of a magnetic field on the growth rate of tetragonal lysozyme crystals

The growth process of tetragonal lysozyme crystals under static and homogeneous magnetic field of 11 T was observed in situ by using an optical microscope which was specially designed and prepared. This optical system, having a spatial resolution of 0.5 μm, was used to measure the growth rate of the lysozyme crystals under 0 and 11 T. The effect of the magnetic field of 11 T was to decrease the growth rate of the crystals. The effect of a magnetic field on the dissolution process of the crystal was also investigated.

Growth of SiGe bulk crystal with uniform composition by directly controlling the growth temperature at the crystal–melt interface using in situ monitoring system

Abstract A SiGe bulk crystal with uniform composition was successfully fabricated by clarifying and controlling the growth parameters at the crystal–melt interface. An apparatus was developed for the direct in situ observation and precise control of the interface parameters such as the temperature and the position. The dynamical change of the growth rate of a SiGe bulk crystal in a temperature gradient can be known by utilizing the apparatus. The growing crystal was continuously pulled down at the pulling rate balanced to the growth rate to keep the interface temperature constant, which resulted in the excellent uniformity of the grown crystal. Our technique opened the possibility to incorporate multicomponent semiconductor substrates to the semiconductor heterostructure technology.

Quasi-liquid layers on ice crystal surfaces are made up of two different phases

Ice plays crucially important roles in various phenomena because of its abundance on Earth. However, revealing the dynamic behavior of quasi-liquid layers (QLLs), which governs the surface properties of ice crystals at temperatures near the melting point, remains an experimental challenge. Here we show that two types of QLL phases appear that exhibit different morphologies and dynamics. We directly visualized the two types of QLLs on ice crystal surfaces by advanced optical microscopy, which can visualize the individual 0.37-nm-thick elementary steps on ice crystal surfaces. We found that they had different stabilities and different interactions with ice crystal surfaces. The two immiscible QLL phases appeared heterogeneously, moved around, and coalesced dynamically on ice crystal surfaces. This picture of surface melting is quite different from the conventional picture in which one QLL phase appears uniformly on ice crystal surfaces.

Interferometric study on the crystal growth of tetragonal lysozyme crystal

Abstract Using a Michelson interferometer, the concentration-gradient layers around a growing hen-egg-white lysozyme, tetragonal crystal were observed. By measuring the concentration distribution and the normal growth rate, the growth mode and the diffusion coefficient of lysozyme molecules were evaluated. The experimental results indicate that the growth is regulated by two-dimensional nucleation in the supersaturation range of 6 ≤ σ surf ≤ 20. The diffusion coefficient was nearly constant, 4.9 ± 0.7 × 10 −11 m 2 s −1 over a wide supersaturation range, differing from that of supersaturated bulk solutions.

Enhancement in the perfection of orthorhombic lysozyme crystals grown in a high magnetic field (10 T)

Orthorhombic crystals of hen egg-white (HEW) lysozyme were grown in a homogeneous and static magnetic field of 10 T. All crystals grown at 10 T were oriented such that their crystallographic c axes were parallel to the magnetic field direction and showed a narrower average full-width at half-maximum (FWHM) of the rocking curve than those grown at 0 T. Rocking-width measurements were made at the BL-10A station at the Photon Factory, Tsukuba, Japan, using a high-resolution vertical-type four-circle diffractometer. Crystal perfection was evaluated using the FWHM of the rocking curve; the effects of the magnetic field on the quality of the crystals were examined by comparison of the FWHM of seven crystals grown at 10 and 0 T. The FWHMs of the reflections along the a, b and c axes decreased by 23.5, 35.3 and 27.8%, respectively, and those of other general reflections decreased by 17.4-42.2% in the crystals grown at high magnetic field. These results clearly showed that a magnetic field of 10 T improved the crystal perfection of the orthorhombic lysozyme crystals. As a result, the maximum resolution of X-ray diffraction increased from 1.3 A at 0 T to 1.13 A at 10 T. The magnetic field also affected the dimensions of the unit cell, increments being 0.2% for the a and c axes and 0.1% for the b axis, respectively. These facts suggest that the application of a high magnetic field during crystallization might result in remarkable enhancements in the diffraction power of protein crystals having magnetic anisotropy.